This application is based on applications Nos. 11-363944 and 11-176208 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a recording medium, specifically to a disc-shaped recording medium on which rows of recording pits are recorded in a concentric or spiral pattern, and a recording/reproducing apparatus for performing a recording or reproducing operation upon the recording medium.
2. Description of the Background Art
In recent years, the amount of data handled by a computer and the like has been on the increase and, accordingly, new high-density recording techniques have been studied. Among the techniques, a recording/reproducing technique which utilizes near-field light (evanescent light) is one of the techniques which have attracted particular attention.
The spot diameter of the near-field light is determined by the size of an opening through which the near-field light penetrates into a near-field environment, independently of a wavelength being used (that is, without being restricted by a diffraction limit). Therefore, the near-field light having a minute diameter may be generated by making the opening less than the wavelength, and the use of this near-field light allows a higher-density recording or reproducing (reading) operation than the conventional technique.
For practical use of an apparatus which performs such a high-density recording and reproducing operation, a high-accuracy tracking technique is required to record data at a high density or to correctly reproduce the data recorded at the high density. For example, it is impossible to put the apparatus into practical use without the capability of a head to track minute recording pits arranged on a recording surface of a recording medium.
Conventional tracking techniques of this type are disclosed in Japanese Patent Application Laid-Open No. 7-225975 (1995), Japanese Patent Application Laid-Open No. 8-321084 (1996), and Japanese Patent Application Laid-Open No. 9-326130 (1997).
For instance, Japanese Patent Application Laid-Open No. 7-225975 discloses a technique such that tracking is performed by detecting pits in the form of wobbled marks (wobbled pits) for tracking servo by using a multiplicity of minute openings arranged in a linear array. In other words, a tracking signal is detected in a multiplicity of circumferential locations of a recording medium.
Japanese Patent Application Laid-Open No. 8-321084 discloses a technique such that tracking is performed by detecting tracking grooves by using a pair of tracking probes adjacent to the opposite ends of a sequence of recording or reproducing probes arranged linearly radially of a recording medium. Like reproducing probes, the tracking probes utilize the near-field light and therefore can achieve accurate position control in the direction of the width of tracks.
Japanese Patent Application Laid-Open No. 9-326130 discloses a method of detecting a tracking signal in such a manner that light is directed from a minute opening at the tip of each of three probes provided in a head in fixedly spaced apart relationship, and the light reflected from a row of recording pits is detected. This method uses a groove part detection signal from the probes disposed on the opposite ends to detect an off-track state, and provides feedback to the operation of the head, thereby achieving proper tracking.
The tracking method disclosed in Japanese Patent Application Laid-Open No. 7-225975 is required to provide a row of minute openings. However, it is very difficult to produce a multiplicity of contiguous openings of about tens of nanometers in size.
The tracking method disclosed in Japanese Patent Application Laid-Open No. 8-321084 requires the additional tracking probes on the opposite sides of the recording or reproducing probes. This increases the size of the head itself and requires the process of producing irregularities to form grooves in the recording medium.
The increase in the size of the head hinders the high-speed drive of the head. Additionally, this tracking method is required to space the pair of tracking probes about tens of nanometers apart from the sequence of recording or reproducing probes. However, it is also very difficult to produce such tracking probes. Moreover, it is difficult to produce the irregularities on the order of tens of nanometers in the surface of the recording medium with good reproducibility.
Similarly, the tracking method disclosed in Japanese Patent Application Laid-Open No. 9-326130 is required to produce the recording medium having irregularities corresponding to the probe units equally spaced on the order of tens of nanometers not greater than the wavelength apart from each other, resulting in great difficulties and increased costs. Furthermore, the fixed spacing between the probes presents another problem in that, when the same probe unit is used for recording and for reproduction, the width of tracks and groove parts of the recording medium are fixed depending on recording/reproducing apparatuses, resulting in the lack of flexibility.
The present invention is intended for a recording medium.
According to the present invention, the recording medium comprises: a recording region for recording a recording pit row; a first track band provided along the recording region; and a second track band provided along the recording region on the opposite side of the recording region from the first track band, the second track band having an optical responsivity different from that of the first track band.
Therefore, the recording medium is configured to distinguishably detect a deviation toward an inner periphery and a deviation toward an outer periphery, to achieve high-accuracy tracking control.
The present invention is also intended for a recording/reproducing apparatus for recording or reproducing a recording pit in or from a recording region of a recording medium, the recording medium further including a first track band and a second track band, the recording region being disposed between the first track band and the second track band, the first track band and the second track band being different in optical responsivity from each other.
According to the present invention, the recording/reproducing apparatus comprises: a reproducing light illumination device for directing reproducing light onto the recording pit; and a tracking light illumination device for directing tracking light onto the recording medium, the tracking light allowing the first track band and the second track band to be included in an illumination area thereof.
Therefore, the recording/reproducing apparatus can perform high-accuracy tracking, is easy to manufacture, and is reduced in size.
In accordance with one aspect of the present invention, in the recording/reproducing apparatus, the tracking light has a diameter greater than that of the reproducing light.
This allows high-density data recording or reproduction while achieving the high-accuracy tracking.
In accordance with another aspect of the present invention, the tracking light illumination device renders the tracking light coaxial with the reproducing light from the reproducing light illumination device to direct the tracking light onto the recording medium.
Therefore, the recording/reproducing apparatus can perform the tracking control using the position of the reproducing light as a center, to perform higher-accuracy tracking.
In accordance with still another aspect of the present invention, the reproducing light illumination device and the tracking light illumination device are formed integrally with each other.
This further reduces the size of the apparatus.
It is therefore an object of the present invention to provide a recording/reproducing apparatus which is capable of performing high-accuracy tracking, easy to manufacture, and reduced in size, and to provide a recording medium suitable for the recording/reproducing apparatus.